Thickness Of Sand Layer Research Articles

INTERACTION BETWEEN BEDDING SAND THICKNESS AND SHELL GROOVE-UNDERSIDE SHAPED CONCRETE BLOCK PAVEMENT

Underside Shaped Concrete Block (USCB) has groove shaped at the underside block surface to produce resistance in horizontal plane and to grip onto the bedding sand layer. However, the horizontal movement of block units is the major problem in pavement due to vehicle braking and accelerated action. This paper presents the laboratory evaluation on vertical and horizontal displacement of shell groove-USCB pavement laid onto different bedding sand layer thickness. A pavement laboratory test was conducted to investigate the interaction between USCB type of the Shell-Rectangular 15 mm (Shell-R15) and bedding sand on three different loose bedding sand layer thicknesses of 50 mm, 70 mm and 90 mm respectively. Then, push-in loading test and horizontal loading test were performed. The results showed that interaction between USCB Shell-R15 and bedding sand layer thickness had significant influence to the vertical and horizontal displacement compared to control of 50 mm loose bedding sand layer thickness. The loose bedding sand layer thickness of 70 mm performed better compared to others.

Remediation of liquefaction effects for an embankment using soil-cement walls: Centrifuge and numerical modeling

Numerical simulations of a centrifuge model test of an embankment on a liquefiable foundation layer treated with soil-cement walls are presented. The centrifuge model was tested on a 9-m radius centrifuge and corresponded to a 28 m tall embankment underlain by a 9 m thick saturated loose sand layer. Soil-cement walls were constructed through the loose sand layer over a 30 m long section near the toe of the embankment and covered with a 7.5 m tall berm. The model was shaken with a scaled earthquake motion having peak horizontal base accelerations of 0.05 g, 0.26 g, and 0.54 g in the first, second, and third events, respectively. The latter two shaking events caused liquefaction in the loose sand layer. Crack detectors embedded in the soil-cement walls showed that they developed only minor cracks in the second shaking event, but sheared through their full length in the last shaking event. The results of the centrifuge model test and two-dimensional nonlinear dynamic simulations are compared for the two stronger shaking events using procedures common in engineering practice. The effects of various input parameters and approximations on simulation results are examined. Capabilities and limitations in the two-dimensional simulations of soil-cement wall reinforcement systems, with both liquefaction and soil-cement cracking effects, are discussed. Implications for practice are discussed.

Static and Seismic Bearing Capacity of Strip Footings on Sand Overlying Clay Soils

This paper examined the ultimate bearing capacity of a strip footing located on a two-layer substrate composed of a sandy soil on a clay layer. The analysis was conducted through discontinuity layout optimization, which is an upper bound limit analysis. This study focused on various factors contributing to the problem, i.e. sand layer internal friction angle, sand layer thickness, clay layer undrained shear strength (cu), unit weight of soil layers (γ), footing width (B) and surcharge pressure (q). Failure in both soil layers was governed by the Mohr–Coulomb criterion. The bearing capacity improves when there are two layers of sand–clay soil in comparison to the homogeneous clay soil. Such improvement is intensified by increasing the internal friction angle and thickness of the sand layer and surcharge pressure. The maximum improvement of the bearing capacity was found in a scenario where the entire failure zone was within the sand layer. The pseudo-static method was used to examine the seismic mode. According to the results, the higher the sand internal friction angle and lower cu/(γB), the lower the decrease in the seismic bearing capacity compared to the static mode. Furthermore, the variations of failure surface in static and seismic modes were investigated. The results obtained in this study were compared against the results of other methods, indicating good consistency.

Experimental Research on Sliding Layer of Cross-Tensioned Prestressed Concrete Pavement

Sliding layer is an important component of cross-tensioned prestressed concrete pavement, friction coefficient of slab bottom is decreased by setting sliding layer, so as to reduce the frictional stress at the bottom of the plate and increase the length of the plate. In order to analyze the effect of “sand + polyethylene film” type sliding layer on friction coefficient, and also recommend the optimal sliding layer parameters, The effect of fineness modulus of sand, thickness of sliding layer and specification of polyethylene film on sliding friction coefficient was discussed through orthogonal test. At the same time, The significance level of sliding layer parameters was assessed on the basis of range analysis. The laboratory test results show that the sliding effect of medium sand is better than that of fine sand and coarse sand, and, the friction coefficient reaches the minimum value with sand layer thickness of 10mm, polyethylene film thickness of 30µm , The significance level of sliding layer parameters ranks as follows: fineness modulus of sand > sand thickness > polyethylene film specification, the test results can be provided for calculating reference for friction stress of the cross-tensioned prestressed concrete pavement.

Fracture Characteristics of Overlying Bedrock and Clay Aquiclude Subjected to Shallow Coal Seam Mining

Some of the coal deposits in the northwest region of China are at relatively shallow depths, covered by a thin layer of bedrock and a thick layer of wind-blown sand. We studied the mechanics and permeability of a clay aquiclude by X-ray diffraction and triaxial loading tests and the fracturing of the overlying bedrock and aquiclude in physical simulation tests. The results indicate that if the bedrock thickness is 90 m or more, the height, distribution pattern, and damage to the water-conducting fractured and caving zones (“belts”) are normal. If the bedrock thickness is 30 m or less, the “three belts make one” phenomenon occurs, and caving extends into the soil layer; the overlying rock is completely perforated by vertical fractures and the collapse spreads to the surface. When the bedrock thickness is between 30 and 90 m, the height of the water-conducting fractured zone is inhibited by the weathered rock and cohesive soil layers, and the height of the “two belts” is significantly decreased. This can be used to prevent and control coal mine water hazard.

Interaction of a rigid beam resting on a strong granular layer overlying weak granular soil: Multi-methodological investigations

In the geotechnical and terramechanical engineering applications, precise understandings are yet to be established on the off-road structures interacting with complex soil profiles. Several theoretical and experimental approaches have been used to measure the ultimate bearing capacity of the layered soil, but with a significant level of differences depending on the failure mechanisms assumed. Furthermore, local displacement fields in layered soils are not yet studied well. Here, the bearing capacity of a dense sand layer overlying loose sand beneath a rigid beam is studied under the plain-strain condition. The study employs using digital particle image velocimetry (DPIV) and finite element method (FEM) simulations. In the FEM, an experimentally characterised constitutive relation of the sand grains is fed as an input. The results of the displacement fields of the layered soil based DPIV and FEM simulations agreed well. From the DPIV experiments, a correlation between the slip surface angle and the thickness of the dense sand layer has been determined. Using this, a new and simple approach is proposed to predict theoretically the ultimate bearing capacity of the layered sand. The approach presented here could be extended more easily for analysing other complex soil profiles in the ground-structure interactions in future.

Analysis of an Attached Sunspace with a Thermal Inertia Floor

An attached sunspace is a partially or fully glazed enclosure, usually located on the first floor, facing south (in the Northern Hemisphere) and adjacent to a conditioned room. Because of the length and orientation of the glazed area, the temperature in the sunspace is usually higher than outside the building. As a Trombe–Mitchel wall, the sunspace has a considerable mass that accumulates thermal energy, but in this case the thermal mass is located in the floor. This capacity to accumulate thermal energy confers the attached sunspace features beyond passive insulation. The sunspace studied in this paper is part of an experimental building located in the North of Spain that was built in the frame of the so-called ARFRISOL project. It consists of a south-facing glazed exterior wall with both clear glass and semi-transparent photovoltaic panels, an intermediate space with a thick layer of sand over a concrete floor, and a partially glazed interior wall. In this paper, a three-dimensional computational model has been implemented to analyse the thermal behaviour inside the sunspace. This analysis takes into account, among other factors, the effects of sun position, incident solar irradiation and temperature both inside and outside.

Behaviors of Embankment on PVD-Improved Haiphong Clay

This paper presents the behaviors of embankments on clay deposits improved by prefabricated vertical drains (PVD) in the north-east coastal plain of Vietnam. The deposit consists of soft Holocene clay (approximately 20 m) and stiff Pleistocene clay (approximately 20 m) on a thick sand layer. PVDs with various spacing were fully installed into the soft clay. Settlement behaviors mostly show a reverse-S curve that consists of three phases: small recompression, rapid and large settlement, and delayed settlement. When the spacing is smaller than 1.0 m, the recompression behavior disappears because of soil disturbance during installation. A nearly elastic behavior is observed during construction; thus, the ratios of lateral displacement to settlement (0.02-0.13) and of the excess pore pressure to the applied pressure (0.1-0.7) are significantly small.

Capacity of skirted foundations in sand-over-clay under combined V-H-M loading

Circular skirted foundations are used widely in the offshore oil and gas industry and renewable energy industry to support subsea infrastructure and founding turbines. The foundations are subjected to combined vertical-horizontal-moment (V-H-M) loadings during operation. This paper describes an extensive investigation of the response of installed circular skirted foundations under operational loadings in sand-over-clay. The overarching aim was to examine the influence of the presence of a sand layer on the combined load capacity. A detailed parametric study was undertaken through small strain finite element analyses, varying the thickness of the sand layer, embedment depth of the foundation (or skirt length), and level of vertical load mobilisation.The effect of the surface sand layer was profound for thicker sand layer of Ts/D > 0.2. Normalised failure envelopes were presented in v-h, v-m and h-m spaces. The FE results on the former two spaces showed unique trend, but not on the latter. New approximating expressions for describing the failure envelopes as a function of the sand layer thickness ratio, skirt length ratio and vertical load mobilisation level were proposed.

A geospatial model to quantify mean thickness of peat in cranberry bogs

Commercial cranberry (Vaccinium macrocarpon Ait.) is cultivated on postglacial deposits of peat capped by 0.3–1m of anthropogenic sand. Despite distinct soil layering, a general paucity of information exists on the physical properties of sand and peat in cranberry bogs. Field measurements and ground penetrating radar (GPR) were used to determine sand and peat thicknesses of 30 cranberry bogs in Massachusetts, United States. GPR-based estimates of peat volume and detailed soil maps were then used to develop a geospatial model of mean peat thickness (L*) in cranberry bogs. The model was applied to 505 cranberry bogs that covered in area of 2827ha. Based on model results and field measurements, average sand and peat thicknesses were 0.5 and 0.9m, respectively. For individual bogs, mean peat thickness exhibited considerable range, with deep peat (L*>1.8m) identified in 22% of the cranberry bogs. Peat was absent (L*=0m) in 26% of the cranberry bogs, which reflected modified upland or glaciolacustrine soils rather than peat. Using average thickness, nutrient concentration, and bulk density of peat and sand layers, a typical cranberry bog stores 750Mgha−1 of carbon, 22,900kgha−1 of nitrogen, and 790kgha−1 of phosphorus. We estimate that peat stores 91% and 78% (by mass) of carbon and nitrogen in cranberry bogs, respectively. In contrast, sand stores the majority of P (78% by mass) in cranberry bogs.

Associations between sediment architecture and liquefaction susceptibility in fluvial settings: The 2010–2011 Canterbury Earthquake Sequence, New Zealand

This study focuses on the sedimentary architecture of sites in the Halswell floodplain (Christchurch, New Zealand) that experienced liquefaction during the 2010–2011 Canterbury Earthquake Sequence. We investigated landforms where ejecta were and were not observed, and define their 3D geometry and sediment characteristics. The first site straddles an abandoned channel of the Halswell River that is overlain by a crevasse splay deposit. The second site is located on the inside bend of an active meander of the river. Both sites were severely affected by liquefaction during the Darfield and Christchurch earthquakes. A suite of techniques was used in the characterization of both sites: detailed geomorphic and liquefaction mapping with DEMs derived from LIDAR; Ground-Penetrating Radar (GPR); paleoseismic trenches; hand-piston cores, radiocarbon dating, grain-size analysis, and cone-penetration tests. Potentially liquefiable sands, based on their grain characteristics and water saturation, were found in many environments within the alluvial setting studied (river channel, point bar deposits and flood plain). The surficial geology of the two study sites is mapped as crevasse splay and point bar deposits. However, the layers that liquefied were at depth within buried abandoned channel and point bar deposits at the Hardwick site, and within buried point bar deposits at the Marchand site. The location of the surface manifestation of liquefaction was characterized by specific geometry of the sedimentary architecture of the alluvial floodplain that facilitated or hindered flow of the slurry of water and entrained sediment towards the surface. On the one hand, the inclined contacts of paleochannel and point bar deposits created pathways for the liquefied material to travel to the surface. On the other hand, in the floodplain, with no ejecta, sand and silty sand layers interfingered with clay lenses, lack the specific geometry that facilitates the ejecta at the surface. The CPT analysis showed that liquefaction ejecta occurred above a thick homogeneous layer of sand, whereas liquefaction ejecta did not occur (or sand blows did not form) where clay lenses were interfingered with sand. At both sites the surface manifestation of liquefaction was mainly located on slightly higher topographic areas, suggesting the topography is an additional controlling factor on the surface distribution of liquefaction ejecta. In summary, the surface manifestation of liquefaction is a result of a specific sediment type that was saturated, sedimentary setting that facilitated flow of fluidized sediment to the surface, and topographic relief prone to cracking.

Historical Nankai-Suruga megathrust earthquakes recorded by tsunami and terrestrial mass movement deposits on the Shirasuka coastal lowlands, Shizuoka Prefecture, Japan

Geological investigations of coastal sediment sequences play a key role in verifying earthquake and tsunami characteristics inferred from historical records. In this paper, we present a multi-proxy investigation of a coastal lowland site facing the Nankai-Suruga megathrust and appraise evidence for tsunamis and earthquake-triggered terrestrial mass movements occurring over the last 800 years. Combining a high-resolution chronology with X-ray computed tomography and analyses of particle size, diatoms, pollen, non-pollen palynomorphs and aerial photographs, we present the most compelling geological evidence of the 1361 CE Kōan (also known as Shōhei) tsunami reported to date from any site along the megathrust. This finding is consistent with either of two recent hypotheses: a single larger rupture of both the Nankai and Tōnankai regions or two smaller ruptures separated by a few days. Enhancing the site chronology using Bayesian age modelling, we verify evidence for inundation during the 1498 CE Meiō tsunami. While previous investigations identified evidence for historically recorded tsunamis in 1605, 1707 and 1854 CE and a storm surge in 1680 or 1699 CE, we encountered a thick sand layer rather than discrete extreme wave deposits in this interval. The overprinting of evidence highlights the potential for geological records to underestimate the frequency of these events. A terrestrial mass movement also deposited a sand layer at the site; radionuclide dating and aerial photographs provide independent confirmation that this may have been triggered by intense shaking in 1944 CE during the most recent great Nankai-Suruga megathrust earthquake.

Vertical uplift resistance of rectangular plate anchors in two layered sand

Based on rigid block collapse mechanism and employing the upper bound theorem of limit analysis, the ultimate vertical uplift resistance of rectangular plate anchors embedded horizontally in two layered sand has been determined. Closed form analytical expressions were derived for computing the vertical uplift resistance in terms of dimensionless uplift factors Fγ and Fq, due to the components of soil unit weight (γ) and surcharge pressure (q) acting on the ground surface, respectively. For given embedment ratios of the anchor, the effect of relative position and thickness of sand layer with higher angle of internal friction (φh) and unit weight (γh), and sand layer with lower angle of internal friction (φl) and unit weight (γl), on the magnitude of Fγ and Fq was studied for different length to width ratio of anchor varying from unity to infinity (square to strip). The solutions obtained from the present theory compare reasonably well with the available data from literature.

Analysis of Piping at Kedung Uling Earthfill Dam, Wonogiri Regency, Central Java Province, Indonesia

Kedung Uling earthfill dam is located between Eromoko and Wuryantoro district, Wonogiri Regency, Central Java, Indonesia. Water leaked from the dam was found and could decrease volume of dam. The objectives of this study are to identify piping and to recommend for solving piping problem. In order to determine the piping direction and litological pattern, investigation of 10 boreholes with various depth has been carried out. This investigation aim to determine characteristics of soil and rock by analyzing 45 cm of thickness of undisturbed samples and to perform permeability test. Permeability test have been conducted by falling head method with 3 different depths. Leaking at the dam was analyzed by Slide 6.0 software. The results indicated that litology of dam have been identified as claystone, sand and tuff. The piping passed under the eastern abutment of the dam is the accumulation of groundwater in the aquifers formed by 8-10 meters thick layer of sand. The total debit of piping is 17,774 cm3/sec. The Factor of safety of piping is under the minimum of standard namely 3,6. Grouting is one of alternative method to minimize the piping. Grouting was simulated to reduce permeability value and increase soil strength. By grouting, the total debit of piping was reduced to 3.314 cm3/sec.

Mapping sand layers in clayey till using crosshole ground-penetrating radar

Fluid transport through clayey tills governs the quantity and quality of groundwater resources in the Northern Hemisphere. This transport is often controlled by a 3D network of macropores (biopores, fractures, and sand lenses) within the clayey till. At present, a nondestructive technique that can map and characterize the sand-lens network does not exist, and full excavation or extensive drilling is therefore the only solution. Acquisition and modeling of crosshole ground-penetrating radar (GPR) may provide the answer to this problem. We collected 1D and 2D crosshole GPR data at a field site in Denmark from four 8 m deep boreholes with horizontal distances varying between 2.64 and 5.05 m. We find that the depth, thickness, and tilt of a coherent sand layer within the clayey till (approximately 0.4–0.6 m thick), as well as the underlying sand formation, can be mapped accurately using GPR data. We efficiently identify the sand as a highly resistive section with high electromagnetic (EM) wave velocities, whereas the clayey till is conductive with lower EM wave velocities. We find that the exact location of the sand occurrences is better delineated by the increase in amplitude than the increase in EM wave velocity. We believe that crosshole GPR may contribute significantly to groundwater protection and contaminant remediation initiatives.

KRUSTPILS DZIRKAĻI HILLFORT. NEW INSIGHTS

KRUSTPILS DZIRKAĻI HILLFORT. NEW INSIGHTS

Geoarchaeological evidence of marshland destruction in the area of Rungholt, present-day Wadden Sea around Hallig Südfall (North Frisia, Germany), by the Grote Mandrenke in 1362 AD

Geophysical and geoarchaeological investigations were carried out in the Wadden Sea of North Frisia (Schleswig-Holstein, Germany) to elucidate major environmental changes that considerably altered the coastal landscape since medieval times. Between the 12th and 14th cent. AD, the present-day tidal flats around the marsh island Hallig Südfall belonged to the historical Edomsharde district and its main settlement Rungholt. For North Frisia, it is well known that during medieval and early modern times, extreme storm surges caused major land losses associated with a massive landward shift of the coastline. Today, cultural traces like remains of dikes, drainage ditches, terps or even plough marks are still visible in the Wadden Sea and provide evidence of the once cultivated marshland.Based on a multi-proxy analysis of sediment cores retrieved from the tidal flat zone around Hallig Südfall and from the Hallig itself, we identified a late medieval paleosol associated with the formerly cultivated marshland most probably belonging to the Edomsharde and local trade centre of Rungholt. Around Hallig Südfall, remains of medieval marsh deposits were found partly eroded and covered by a coarse-grained high-energy deposit including abundant shell debris and artefacts. Based on sedimentological, micropaleontological, geochemical and geochronological data, we conclude that these deposits are associated with the 1st Grote Mandrenke (or St. Marcellus’ flood), an extreme storm surge event in 1362 AD. Our results, for the first time, provide geological evidence of this 1362 AD storm surge for the Wadden Sea of North Frisia. Moreover, marshland on Hallig Südfall dating to the 17th-18th cent. AD was found covered by a thick layer of storm surge sand and shell debris which seems to be associated with one of the major storm event that hit the German North Sea coast in modern times, e.g. the 2nd Grote Mandrenke (or Burchardi flood) in 1634 AD or the Christmas flood in 1717 AD.

Superhydrophobic sand grains structured with aligned Cu(OH)2 nano-needles for efficient oily water treatment

Desert sand as an abundant natural resource rarely has been reconsidered and reutilized due to its superhydrophilicity. Aiming at the combination of super-wettability with sand resource, we successfully design the aligned Cu(OH)2 nano-needles on the sand grain surfaces through a skillful strategy and conferred superhydrophobic properties on them in this study. The water contact angle and rolling angle are shown to be ~158° and ~6°, which break our traditional understanding towards desert sand, i.e., superhydrophilicity. More importantly, the selective superhydrophobic-superoleophilic wettability and the cavities between nano-needles and sand grains allow the sand to be a good candidate for efficient oily water treatment. The as-prepared superhydrophibic sand can not only absorb light oils from water surface, but separate heavy oils from oil/water mixtures. The speed of oil/water separation is up to 16,985Lm−2h−1 when a 0.35cm thickness of superhydrophobic sand layer is used. Significantly, it exhibits both high separation rate and high separation efficiency (>99.5%). The as-prepared superhydrophobic sands are expected to become a new candidate of highly efficient oil/water separation material and to realize the reutilization of desert sand resource.

Effects of slope gradient on hydro-erosional processes on an aeolian sand-covered loess slope under simulated rainfall

The aeolian sand-covered loess slope of the Wind-Water Erosion Crisscross Region of the Loess Plateau in China may play a key role in contributing excessive sediment to the Yellow River. Understanding its hydro-erosional processes is crucial to assessing, controlling and predicting soil and water losses in this region and maintaining the ecological sustainability of the Yellow River. Simulated rainfall (intensity 90mmh−1) was used to investigate the runoff and soil loss from loess slopes with different slope gradients (18%, 27%, 36%, 47%, and 58%) and overlying sand layer thicknesses (0, 5 and 10cm). As compared with uncovered loess slopes, an overlying sand layer delayed runoff production, reduced cumulative runoff and increased cumulative soil loss, as well as enhancing variations among slope gradients. Cumulative runoff and soil loss from the sand-covered loess slopes increased with increasing slope gradients and then slightly decreased, with a peak at about 47% gradient; they both were greater from the 10-cm sand-covered loess slope than from the 5-cm except for with 18% slope gradient. In general, differences in cumulative runoff between sand layer thicknesses became smaller, while those in cumulative soil loss became larger, with increasing slope gradient. Runoff and soil loss rates on the sand-covered loess slopes exhibited unimodal distributions during the rainstorms. Maximum values tended to occur at the same rain duration, and increased considerably with increasing slope gradient and sand layer thickness on slopes that were less than 47%. Liquefaction process might occur on the lower loess slopes covered with thinner sand layers but failures similar to shallow landslides might occur when the sand layer was thicker on steeper slopes. The presence of an overlying sand layer changed the relationship between runoff and soil loss rates during intense rainstorms and this change varied with different slope gradients. Our results demonstrated that the effects of slope gradient on hydro-erosional processes on the sand-covered loess slopes were important and vary with changing sand thickness. These effects should be considered when assessing and predicting soil losses from such slopes in the study region and from similar slopes elsewhere.

Bearing Capacity of Foundations with Inclusion of Dense Sand Layer over Loose Sand Strata

The lower- and upper-bound finite-element limit analysis in conjunction with second-order conic programming (SOCP) was used to estimate the ultimate bearing capacity of strip and circular footings with an inclusion of a layer of dense sand over existing loose sand strata. The analysis followed the Mohr-Coulomb yield criterion and an associated flow rule. The results are expressed in terms of an efficiency factor that increases quite significantly with increases in the (1) thickness and (2) friction angle of the upper densified layer. While keeping the same thickness of the upper dense sand layer, the circular footing exhibits greater efficiency-factor values as compared to strip footing. The numerical results compare well with data available from the literature. (C) 2017 American Society of Civil Engineers.